Record Iris review fixes, validation, and consolidated checkout

docs/LAYOUT_LOG.md

@@ -6,12 +6,60 @@ nothing here is rediscovered. Each entry says who found it and when.
 it (settled design, the measurement method) belongs in `docs/LAYOUT.md`, and
 the current plan is in `docs/HANDOFF.md`.
 
-## What the review of #19 found (2026-09-19)
+## Follow-up implementation review (2026-09-19)
 
-Read at `cadfba0` in the `iris/` submodule of this checkout, which is the
-same commit as `layout/one-ask`. `cargo fmt --all --check`, clippy
-`-D warnings` and the 123-test suite are clean there, so both defects below
-are live behaviour rather than anything the tests say.
+The ask/place split, window-unit frames, exact validity preimages, and
+bottom-up dirty settling implement the settled design. Keep this approach.
+It does not guarantee one body call per widget: an unhinted descendant that
+reports leftover weight still needs a room ask and a slot ask. The explicit
+measurement redesign remains deferred until an app screen justifies it.
+
+The fixes below are on `layout/one-ask` in `/home/bob/repos/iris`:
+
+- A collapsed share advances both span cursors. The regression covers one
+  and two collapsed children in all four directions.
+- A masking widget owns a mask reference and reclaims its existing slot on
+  redraw. Primitives retain their own references. Removing the mask,
+  undrawing its owner, freeing the widget, and replacing the root release
+  ownership; a changed inherited mask rejects drawing reuse. Tests check
+  actual primitive mask indices, movement with and without a region node,
+  child draw counts, clip removal/addition, and empty-mask slot reuse.
+- **A further handover defect:** `draw_inner` saved the old parent only
+  after a redraw replaced `ActiveData`. The old parent therefore kept the
+  child in its list and could undraw the subtree after its new parent drew
+  it. Capture the old parent before replacing the record. A branch-switch
+  regression reproduces disappearing content when its new parent owns a
+  region node, and also checks the ordinary reuse path.
+
+The mask and handover tests fail on the reviewed code and pass with the
+fixes. The mask fix preserves child reuse rather than redrawing descendants
+on every mask repaint. No naming sweep or rounding-policy change is included.
+
+Validation: workspace tests with and without diagnostics, the release fast
+oracle, and all three prescribed seed scans pass. Comparing 34,488 cold
+boxes against `cadfba0` finds 650 changes; withholding just the collapsed-slot
+fix reproduces the baseline exactly. This is an expected geometry correction,
+not a cost-only change whose dump should remain identical. The tabs example
+and an exact 400 px collapsed-share fixture were rendered and inspected.
+
+Two test-harness savings leave the random stream and coverage unchanged:
+`generated` constructs one plan per seed for its sixteen scenarios, and the
+warm/cold comparison constructs its diagnostic ancestry lookup only after
+finding a mismatch. No overall speedup is claimed; no deep profile was run.
+
+**Integration is larger than an API rename.** The app's pinned `32f6ad8`
+has 45 commits not reachable from this review branch. In particular, the
+app's nested/shape masks and shared `Ui` ownership are absent here: #19's
+mask is still a single rectangle and `set_mask` rejects nested masks. Keep
+the app pin until those existing capabilities have been integrated. The
+"Masks" and "UI ownership" sections of `LAYOUT.md` describe the app-side
+implementation, not everything already present on the upstream review branch.
+
+## Original review of #19 at `cadfba0` (2026-09-19)
+
+The original review read `cadfba0`, then the tip of `layout/one-ask`.
+`cargo fmt --all --check`, clippy `-D warnings` and the 123-test suite were
+clean there. These are the original failures, fixed by the follow-up above.
 
 ### A span misplaces the slot after a collapsed `leftover` child
 
@@ -80,11 +128,11 @@ per-widget mask slot kept across redraws, the way `UiRenderState::move_slot`
 already keeps a move entry, so the index is stable and `reposition` goes on
 updating the one the descendants name.
 
-### Neither path has a test
+### Regression coverage
 
-The suite passes with and without both fixes. A span case belongs in
-`tests/cases/layout.rs` and a mask-reuse case in `tests/cases/retained.rs`
-when they land.
+Both paths now have regressions in `tests/cases/layout.rs` and
+`tests/cases/retained.rs`; the follow-up above records the additional cases.
+The descriptions above preserve the original failure at `cadfba0`.
 
 ### Clarity, in the order worth doing